40 C.F.R. § 1620.9
Final denial of an administrative claim must be in writing and sent to the claimant, his or her agent, attorney, or other legal representative by certified or registered mail. The notification of final denial may include a statement of the reasons for the denial. However, it must include a statement that, if the claimant is dissatisfied with the CSB action, he or she may file suit in an appropriate United States District Court not later than 6 months after the date of mailing of the notifications, along with the admonition that failure to file within this 6 month timeframe could result in the suit being time-barred by the controlling statute of limitations. In the event that a claimant does not hear from the CSB after 6 months have passed from the date that the claim was presented, a claimant should consider the claim denied and, if desired, should proceed with filing a civil action in the appropriate U.S. District Court.
40 C.F.R. § 1620.9